Internet DRAFT - draft-zheng-netconf-udp-pub-channel
draft-zheng-netconf-udp-pub-channel
NETCONF G. Zheng
Internet-Draft T. Zhou
Intended status: Standards Track A. Clemm
Expires: February 25, 2018 Huawei
August 24, 2017
UDP based Publication Channel for Streaming Telemetry
draft-zheng-netconf-udp-pub-channel-01
Abstract
This document describes a UDP-based publication channel for streaming
telemetry use to collect data from devices. A new shim header is
proposed to facilitate the distributed data collection mechanism
which directly pushes data from line cards to the collector. Because
of the lightweight UDP encapsulation, higher frequency and better
transit performance can be achieved.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 25, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
4. UDP Transport for Publication Channel . . . . . . . . . . . . 6
4.1. Data Format . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Options . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Reliability Option . . . . . . . . . . . . . . . . . 8
4.2.2. Authentication Option . . . . . . . . . . . . . . . . 9
4.3. Data Encoding . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Operational Considerations . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix A. An Appendix . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Streaming telemetry refers to sending a continuous stream of
operational data from a device to a remote receiver. This provides
an ability to monitor a network from remote and to provide network
analytics. Devices generate telemetry data and push that data to a
collector for further analysis. By streaming the data, much better
performance, finer-grained sampling, monitoring accuracy, and
bandwidth utilization can be achieved than with polling-based
alternatives.
Sub-Notif [I-D.ietf-netconf-subscribed-notifications] and YANG-Push
[I-D.ietf-netconf-yang-push] defines a mechanism that allows a
collector to subscribe to updates of YANG-defined data that is
maintained in a YANG [RFC7950] datastore. The mechanism separates
the management and control of subscriptions from the transport that
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is used to actually stream and deliver the data. Two transports have
been defined so far, NETCONF [RFC6241] and RESTCONF [RFC8040].
While powerful in its features and general in its architecture, in
its current form the mechanism needs to be extended to stream
telemetry data at high velocity from devices that feature a
distributed architecture. Specifically, there are two aspects that
need to be addressed:
1. The transports that have been defined so far, NETCONF and
RESTCONF, are ultimately based on TCP (Transmission Control
Protocol) and lack the efficiency needed to stream data
continuously at high velocity. A lighter-weight, more efficient
transport, e.g. a transport based on UDP (User Datagram Protocol)
is needed.
* Firstly, data collector will suffer a lot of TCP connection
from, for example, many line cards equipped on different
devices.
* Secondly, as no connection state needs to be maintained, UDP
encapsulation can be easily implemented by hardware which will
further improve the performance.
* Thirdly, because of the lightweight UDP encapsulation, higher
frequency and better transit performance can be achieved,
which is important for streaming telemetry.
2. The current design involves a single push server. In the case of
data originating from multiple line cards, the design requires
data to be internally forwarded from those line cards to the push
server, presumably on a main board, which then combines the
individual data items into a single consolidated stream. This
centralized data collection mechanism can result in a performance
bottleneck, especially when large amounts of data are involved.
What is needed instead is support for a distributed mechanism
that allows to directly push multiple individual substreams, e.g.
one from each line card, without needing to first pass them
through an additional processing stage for internal
consolidation, but still allowing those substreams to be managed
and controlled via a single subscription.
This document specifies a distributed data collection mechanism which
can directly push data from line cards to a collector by using a UDP
based publication channel. Specifically, a higher-performance
transport option for YANG-Push that leverages UDP is specified.
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While this document will focus on the data publication channel, the
subscription can be used in conjunction with the mechanism proposed
in [I-D.ietf-netconf-yang-push] with necessary extensions.
Although the distributed data streaming from device line cards is one
typical scenario that the proposed UDP based publication channel can
be useful, the proposal is general enough to fit more scenarios that
require UDP transport for data collections, e.g. the IoT (Internet of
Things) use case.
2. Terminology
Streaming telemetry: refers to sending a continuous stream of
operational data from a device to a remote receiver. This provides
an ability to monitor a network from remote and to provide network
analytics.
Component subscription: A subscription that defines the data from
each individual entity which is managed and controlled by a single
subscription server.
Subscription agent: An agent that streams telemetry data per the
terms of a component subscription.
3. Solution Overview
The typical distributed data collection solution is shown in figure
1. The subscription server located in the main board receives the
subscription requests or configurations. It may be colocated, not
necessary, with a NETCONF server which interacts with outside
clients. When receiving a subscription request, the subscription
server decomposes the subscription into multiple component
subscriptions, each involving data from a separate internal telemetry
source, for example a line card. The component subscriptions are
distributed within the device to the subscription agents located in
line cards. Subsequently, each line card generates its own stream of
telemetry data, collecting and encapsulating the packets per the
component subscription and streaming it to the designated data
collector.
The publication channel supports the reliable data streaming, for
example for some alarm events. The subscriber has the option of
deducing the packet loss and the disorder based on the information
carried by the notification data. And the subscriber will decide the
behavior to request retransmission. The subscriber can send the
retransmission request to the subscriber server for further
processing.
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Subscription server and subscription agents interact with each other
in several ways:
o Subscription agents need to have a registration or announcement
handshake with the subscription server, so the subscription server
is aware of them and of lifecycle events (such as subscription
agents appearing and disappearing).
o The subscription server relays the component subscriptions to the
subscription agents.
o The subscription agents indicate status of component subscriptions
to the subscription server. The status of the overall "master"
subscription is maintained by the subscription server. The
subscription server is also responsible for notifying the
subscriber in case of any problems of component subscriptions.
The rest of the draft describes the UDP based publication channel.
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retransmission + +
request | | subscription
+------------------------+
| | | Main Board|
| +--v----v--------+ |
| | subscription | |
| | server | |
| +--+----+-----+--+ |
| | | | | internal
+------------------------+ subscription
| | | distribution
+---------------+ | +--------------+
| | |
+------------------+ +------------------+ +------------------+
| | | | | | | | |
| +-------v------+ | | +------v-------+ | | +-----v--------+ |
| | subscription | | | | subscription | | | | subscription | |
| | agent | | | | agent | | | | agent | |
| +--------------+ | | +--------------+ | | +--------------+ |
| Line Card 1 | | Line Card 2 | | Line Card n |
+---------+--------+ +--------+---------+ +----------+-------+
| | |
| | Publication Channel |
+--------------+ | +-----------------+
| | |
+-v-----v-----v-+
| |
| Collector |
| |
+---------------+
4. UDP Transport for Publication Channel
In [I-D.voit-netconf-notification-messages], the transport
independent message header is proposed for the notification use. The
following shim header refers to and implements that message header
definition.
4.1. Data Format
The data format of the UDP based based publication transport is shown
as follows.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------------------------------------------------------+
~ UDP Header ~
+-------+---------------+-------+-------------------------------+
| Vers. | Flag | Rsvd | Length |
+-------+---------------+-------+-------------------------------+
| Notification-Time |
+---------------------------------------------------------------+
| Message-Generator-ID |
+---------------------------------------------------------------+
~ Options ~
+---------------------------------------------------------------+
~ Message Content ~
+---------------------------------------------------------------+
Right after the UDP header, a simple inform header is attached to
carry the necessary information with regard to the streaming mode.
o The Vers. field represents the PDU (Protocol Data Unit) encoding
version. The initial version value is 0.
o The Flag is a bitmap indicating what features this packet has and
the corresponding options attached. Each bit associates to one
feature and one option data. When the bit is set to 1, the
associated feature is enabled and the option data is attached.
The sequence of the presence of the options follows the bit order
of the bitmap. In this document, 2 flags are specified as
follows:
* bit 0, the reliability flag;
* bit 1, the authentication flag;
* other bits are reserved.
o The Length field is the total length of the message, measured in
octets, including message header.
o The Message-Generator-ID is a 32-bit identifier of the process
which created the message notification. This allows
disambiguation of an information source, such as the
identification of different line cards sending the notification
messages.
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o The Notification-Time, is the time at which the message leaves the
exporter, expressed in seconds since the UNIX epoch of 1 January
1970 at 00:00 UTC, encoded as an unsigned 32-bit integer.
o The Options is a variable-length field. The details of the
Options will be described in the respective sections below.
After the inform header is the real content which is encoded. The
actual encoding is based on the subscription, e.g., in binary with
GPB [1] or CBOR [RFC7049].
4.2. Options
The order of packing the data fields in the Options field follows the
bit order of the Flag field.
4.2.1. Reliability Option
The UDP based publication transport described in this document
provides two streaming modes, the reliable mode an the unreliable
mode, for different SLA (Service Level Agreement) and telemetry
requirements.
In the unreliable streaming mode, the line card pushes the
encapsulated data to the data collector without any sequence
information. So the subscriber does not know whether the data is
correctly received or not. Hence no retransmission happens.
The reliable streaming mode provides sequence information in the UDP
packet, based on which the subscriber can deduce the packet loss and
disorder. Then the subscriber can decide whether to request the
retransmission of the lost packets.
In most case, the unreliable streaming mode is preferred. Because
the reliable streaming mode will cost more network bandwidth and
precious device resource. Different from the unreliable streaming
mode, the line card cannot remove the sent reliable notifications
immediately, but to keep them in the memory for a while. Reliable
notifications may be pushed multiple times, which will increase the
traffic. When choosing the reliable streaming mode or the unreliable
streaming mode, the operate need to consider the reliable requirement
together with the resource usage.
When the reliability flag bit is set to 1 in the Flag field, the
following option data will be attached
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------------------------------------------------------+
| Notification ID |
+---------------------------------------------------------------+
| Previous Notification ID |
+---------------------------------------------------------------+
The notification ID is generated continuously by the message
generator. Different subscribers share the same notification ID
sequence. Current ID and previous ID will be added in the packets.
For example, there are two subscriber A and B,
o Notification IDs for the generator are : [1, 2, 3, 4, 5, 6, 7, 8,
9], in which Subscriber A subscribes [1,2,3,6,7] and Subscriber B
subscribes [1,2,4,5,7,8,9].
o Subscriber A will receive : [0,1][1,2][2,3][3,6][6,7].
o Subscriber B will receive : [0,1][1,2][2,4][4,5][5,7][7,8].
4.2.2. Authentication Option
When the authentication flag bit is set to 1 in the Flag field, a 24
octets data field will be included in the Options. The message is
signed, and the signature is filled in the 24 octets Authentication
Option field. So that a receiver can verify the authenticity of the
message.
HMAC [RFC2104] defines a mechanism for message authentication using
cryptographic hash functions. Any message digest algorithm can be
used, but the cryptographic strength of HMAC depends on the
properties of the underlying hash function. As suggested by
[RFC6151], new protocol designs should not employ HMAC-MD5 [RFC2202].
Alternatives to HMAC-MD5 include HMAC-SHA256 [RFC4231] and AES-CMAC
[RFC4493].
Implementations permit multiple acceptable algorithms, while the
HMAC-SHA256 algorithm is mandatory in this document. The resulting
message digest (output of HMAC) is truncated to 24 octets, which is
the 192 leftmost bits of the HMAC computation, to fit the size of the
Authentication Option field. It is recommended in [RFC2104] that the
truncated output length should be not less than half the length of
the hash output to match the birthday attack bound.
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4.3. Data Encoding
Subscribed data can be encoded in GPB, CBOR, XML or JSON format. It
is conceivable that additional encodings may be supported as options
in the future. This can be accomplished by augmenting the
subscription data model with additional identity statements used to
refer to requested encodings.
5. IANA Considerations
TBD
6. Operational Considerations
While efficient, UDP has no build-in congestion-avoidance mechanism.
It is not recommended to use the UDP based publication channel over
congestion-sensitive network paths. The deployments require the
communications from exporters to collectors are always congestion
controllable, i.e., the transport is over dedicated links or the
streaming rate can be limited.
7. Security Considerations
The security of the UDP based publication channel depends on the
subscription channel. Typically, both NETCONF and RESTCONF support
the secure configuration of the private key for the publication
channel. So that the message data can be encrypted by using
symmetric key algorithms.
8. Acknowledgements
The authors of this documents would like to thank Eric Voit, Tim
Jenkins, and Huiyang Yang for the initial comments.
9. References
9.1. Normative References
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997, <https://www.rfc-
editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
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[RFC2202] Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
SHA-1", RFC 2202, DOI 10.17487/RFC2202, September 1997,
<https://www.rfc-editor.org/info/rfc2202>.
[RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA-
224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512",
RFC 4231, DOI 10.17487/RFC4231, December 2005,
<https://www.rfc-editor.org/info/rfc4231>.
[RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
2006, <https://www.rfc-editor.org/info/rfc4493>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
9.2. Informative References
[I-D.ietf-netconf-subscribed-notifications]
Voit, E., Clemm, A., Prieto, A., Nilsen-Nygaard, E., and
A. Tripathy, "Custom Subscription to Event Notifications",
draft-ietf-netconf-subscribed-notifications-03 (work in
progress), July 2017.
[I-D.ietf-netconf-yang-push]
Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-
Nygaard, E., Bierman, A., and B. Lengyel, "Subscribing to
YANG datastore push updates", draft-ietf-netconf-yang-
push-08 (work in progress), August 2017.
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[I-D.voit-netconf-notification-messages]
Voit, E., Bierman, A., Clemm, A., and T. Jenkins,
"Notification Message Headers and Bundles", draft-voit-
netconf-notification-messages-01 (work in progress), July
2017.
9.3. URIs
[1] https://developers.google.com/protocol-buffers/
Appendix A. An Appendix
Authors' Addresses
Guangying Zheng
Huawei
101 Yu-Hua-Tai Software Road
Nanjing, Jiangsu
China
Email: zhengguangying@huawei.com
Tianran Zhou
Huawei
156 Beiqing Rd., Haidian District
Beijing
China
Email: zhoutianran@huawei.com
Alexander Clemm
Huawei
2330 Central Expressway
Santa Clara, California
USA
Email: alexander.clemm@huawei.com
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